Tropical fish guides can help you choose how to populate your aquarium. These books will explain the various kinds of species of fish out there. They will also go into some details on their preferred habitats, whether or not they are placid or violent by nature etc. You should also manage to find out what species can co-habit and which types to avoid altogether in a mixed environment.
The more common types of tropical fish can be found at most pet shops and your nearby fish tank outlet. Most people will need some Neon Tetras because they are attractive with their bright colored bodies. They are also an extremely tranquil fish which means you don't need to worry about them fighting.
The tropical fish guides may also give you some guidelines regarding how to set up your aquarium. The most obvious is whether or not you will use freshwater or salt water but this is not the sole consideration. Some types of fish are stone dwellers and to grow they require some of their natural environment in the water. Others are used to staying in the Coral reef so would prefer a tank with a bit of coral material in it. You ought to be trying to replicate their natural habitat whenever possible and all issues you might have must be answered at least in part by the books.
Your guide can even give you some direction on the size of tank necessary. Some tropical fish need more space than others and one of the classic mistakes newbies will make is to buy way too many fish for a small tank. The water will need to be regularly checked for nitrate levels. The position of the tank is very important as you cannot have fish situated in direct sunlight or over a heater.
There is a great deal to owning fish and reading some tropical fish guides is only the first step of your education!